Transport and stability of long‐pulse relativistic electron beams in UV laser‐induced ion channels

Abstract

Results are presented for the first experiments in which long‐pulse (0.4–1 μsec), relativistic (0.8 MV) electron beams have been transported in the ion focused regime (IFR) in ion channels formed in low pressure diethylaniline gas by means of KrF excimer laser‐induced ionization. These experiments demonstrate that the most efficient (50%–80%) and longest pulse (0.6 μsec) e‐beam transport is obtained with laser‐induced channels over a very narrow gas pressure range (0.3–1.7 mTorr). Higher than optimal pressures cause excess e‐beam‐induced ionization and instability of the electron beam. At lower pressures, the laser‐induced ion channel density is insufficient for initial e‐beam guidance. Transverse oscillations of the electron beam have been measured at a frequency close to that predicted for the ion hose instability. The growth length and wavelength of the transverse oscillations are comparable to the betatron wavelength, further suggesting that these oscillations result from the ion hose instability.